1. Technical Field
The present invention relates generally to rotary cutters for the print-processing industry. More specifically, the present invention relates to rotary cutters including a pair of knives separated by an adjustable cutting gap.
2. Related Art
Known rotary cutters typically include an upper knife and a lower knife, both of which are mounted on rotating shafts. The upper knife and lower knife are separated by a cutting gap that can be adjusted by an adjusting mechanism that allows one or both of the knives to be moved along the axis of its shaft. Typically, the cutting gap is adjusted manually by first moving one of the knives from a starting position to a zero position (i.e., where there is no cutting gap), and then moving the knife in the opposite direction from the zero position to the desired cutting position. A certain mechanical knowledge is necessary for making the correct adjustment. Typically, a skilled mechanic is consulted for this adjustment. A rotary cutter as described above is disclosed in European Patent Application No. 03 405 621.8, filed Aug. 28, 2003, which is owned by the applicants of the present invention, and incorporated herein by reference.
To achieve optimum cutting results with the above-described type of rotary cutter, the cutting gap between the upper knife and the lower knife must be adjusted, for example, in the range of 0.03 mm to 0.035 mm. This adjustment is commonly made by way of an adjusting spindle having vernier, wherein either the upper knife or the lower knife is adjusted. The adjustment of the cutting gap must be done with extreme precision to prevent a cutting gap that is either too wide or too narrow. For example, if the cutting gap is too wide, the cutting quality will be insufficient. If the cutting gap is too narrow, the knife blades can break, especially the upper knife blade which is usually quite expensive.
European Patent No. 1 177 833 A1 discloses a rotary cutting machine in which the upper knife blade and the lower knife blade are electrically insulated relative to one another, such that, if the two knives come into contact during the cutting operation, a circuit is closed and an optical or acoustic signal is emitted. Usually, such a contact between the knives is caused by strong heat expansion. The optical or acoustic signal is intended to trigger a shut down of the machine when the blades make contact, thus avoiding damage to the blades. However, an unintended signal may be emitted if the circuit is closed, for example, because of oil in the cutting gap. This type of rotary cutting machine also experiences the aforementioned disadvantages in adjusting the cutting gap.
Therefore, there remains a need in the art for a rotary cutter that overcomes the shortcomings of conventional solutions.